I am looking to power a fairly large load (about 15amps), but want to give it only about 7 volts under normal conditions and then switch it to full voltage (car output at about 14.8 volts) when a certain condition is met.

Whats the easiest andd most economical way to do this?

Probably a relay. Depending on what your condition is, have it trigger the relay which would kick in a second battery. Or if you have a battery putting out 14.8 volts and you run it through a restricted line so it only can get 7, then trigger the relay to open another line allowing the full voltage.

I was going to use relays to kick the full line voltage in, but what kind of resistor will take a 15 amp load?

Good question, you may have to do some searching for that one. Another idea would be to configure a couple relays to switch a pair of batteries from running in series to running in parallel. Although I see the potential of a short from that, I think it would be feasible.

This is for running a very large IC Pump, I didnt want to come out and way that but it will help for determining the right way to supply power to it. I want to have a safe way to drop the pump speed when not on the throttle and then kick it in the *** when the motor makes boost.

What about just getting an IC controller? IC Controller Something kinda like this? It runs the pump at 5% during idle and them 100% once you hit 50% throttle, which is what you want when you think about it. If it doesn't start moving water until you hit boost, your going to be making the heat FAST, and the water is going to take longer to get moving to cool it down.

Thats only rated for about half the amperage i am looking to draw, I said a VERY LARGE water pump

Would something like this be able to power any DC motor?

I emailed Meziere to ask about using a PWM speed controller with their pumps and they said it should be fine, so that'* the plan, now I just need money. . .. lots of money.

From 96-99 there was a fuel pump module in the trunk. It runs the pump at about 8 volts most of the time and when you kick it you get full voltage.

Being a fuel pump item, I'd figure that should be good for at least 15amps.

And yes..I think I do.

Sweet, that would make things easy too, I guess when I get around to intercooling I will have several options. Thanks Bill